In general, in combustion furnaces (combustion systems) typified by industrial furnaces such as a steel furnace, a deodorizing furnace and a heating furnace, a combustion control is performed by a combustion controlling device while monitoring a combustion state of a burner disposed in the combustion furnace, a furnace temperature, a pressure of a combustion air, and a pressure of a fuel to be supplied to the burner, to thereby ensure safe combustion. For example, the combustion controlling device performs a safety control that determines whether a flame caused by the burner is present, or not, with the use of a flame detector, and stops the supply of fuel to a combustion furnace when the flame is not detected (for example, refer to Patent Document 1).